This invention relates to electron-beam exposure machines for accurate submicron lithography, particularly for writing on optical and x-ray mask surfaces or directly on semi-conductor surfaces.
Some electron-beam writing pattern systems scan with a single beam for writing individual pixels on the resist layer of a semiconductor workpiece. Each pixel requires a combination of a range of an exposure time and current density. This pixel by pixel approach limits the throughput of such systems.
Some industrial writing-pattern systems use larger, variably shaped apertures to write patterns. Such systems have the disadvantages of producing the same current density with each shape, so that changing the shape area results in current changes and hence variation in bulk space charge within the electron beam. This may alter the plane of best focus and allow proper focusing of only one area. AS the shape size increases, electron to electron interaction increases and the beam broadens and the edge sharpness decreases. Also, the continually changing beam current makes it difficult to maintain a stable column.
U.S. Pat. No. 4,153,843 discloses a system that forms the patterns from an m.times.n array of fixed identical spots each of which receives on or off signals to produce the desired pattern. Such a system requires complex electronic drives to form the desired patterns. Also the system causes the beams from the apertures to recross at a focus point.
An object of the invention is to overcome these disadvantages.
Another object of the invention is to improve electron-beam pattern writing systems.
Another object of the invention is to improve the throughput of electron-beam pattern writing systems.